block_sample.rb

def call_block
  puts "start"
  yield "foobar" if block_given?
  puts "end"
end

def call_block2(&block)
  puts "start"
  block.call("foobar")
  puts "end"
end

call_block do |str|
  puts "here"
  puts str
  puts "here"
end

# start
# here
#   foobar
# here
# end

f = File.open("myfile.txt", 'w')
f.write("Lorem ipsum dolor sit amet")
f.write("Lorem ipsum dolor sit amet")
f.close

# using block
File.open("myfile.txt", 'w') do |f|
  f.write("Lorem ipsum dolor sit amet")
  f.write("Lorem ipsum dolor sit amet")
end

# with code block

def send_message(msg)
  connection do |socket|
    socket.puts "foobar"
    socket.gets
  end
end

def connection
  socket = TCPSocket.new(@ip, @port)
  yield socket         # 用块的方式把外层的参数 闭包传到块里面
  ensure
    socket.close
  end
end

class SortedList

  def initialize
    @data = []
  end

  def <<(element)
    (@data << element).sort!
  end

  def each
    @data.each {|e| yield(e)}
  end
end

File.open("some.txt"){|f| f << "some words"}

"this is a string".instance_eval do
  "O hai, can has reverse? #{reverse} . "
end

foo = Hash.new{ |h,k| h[k] = []}

require 'socket'

class Client
  def initialize(ip = "127.0.0.1", port = "3003")
    @ip = ip
    @port = port
  end

  def send_message(msg)
    connection do |socket|
      socket.puts(msg)
      response = socket.gets
    end
  end

  def receive_message
    connection do |socket|
      response = socket.gets
    end
  end

  private

  def connection
    socket = TCPSocket.new(@ip, @port)
    yield(socket)
  ensure
    socket.close if socket
  end
end